1. Field of the Invention
The invention relates in general to a liquid crystal display device and a configuration of common electrode thereof, and more particularly to liquid crystal display device and a configuration of common electrode thereof having electrostatic discharge protection circuits.
2. Description of the Related Art
Electrostatic discharge is an accumulation of static electricity and occurs when electrostatic charges are shifted between different objects. The occurrence of electrostatic discharge is instant and is measured at nano-seconds. Within such a short instance, the static electricity will have currents as high as several amperes. When such a high current flows through a semiconductor, the semiconductor will be damaged. For example, in an ordinary thin-film-transistor (TFT) liquid crystal display device, the common electrode on the glass substrate is formed on a first metal layer, while the data line is formed on a second metal layer. The metal of the first layer and the metal of the second layer are separated by an oxide layer. When the above static electricity occurs to the data line and the common electrode, the high current generated by the static electricity would penetrate the oxide layer when flowing through the crossing area between the data line and the common electrode and cause short circuits to the first metal layer and the second metal layer.
Referring to FIG. 1, a repairing configuration of a conventional liquid crystal display device is shown. The liquid crystal display device 100 has a glass substrate 102. The glass substrate 102 has several data lines DL(1)˜DL(N), a common electrode COM, several electrostatic discharge protection circuits ESD 104(1)˜104(N) and a pixel array 106 disposed thereon, wherein N is a positive integer. The electrostatic discharge protection circuits 104(1)˜104(N) are respectively bridged between their corresponding data lines DL and the common electrode COM. The electrostatic discharge protection circuits 104(1)˜104(N) are used for resolving the electrostatic discharge occurring on the data lines DL or the common electrode COM. The pixel array 106 includes a number of pixels (not shown in FIG. 1). The pixels are electrically connected to their corresponding data lines DL, respectively. The two sides of the common electrode COM are both coupled to the common electrode voltage Vcom. The routings of the data lines DL(1)˜DL(N) on the glass substrate 102 all cross over the common electrode COM. When static electricity occurs to the second data line DL(2), the high current generated by the static electricity would cause short circuit to the second data line DL(2) and the common electrode COM at a short circuit point S1 shown in FIG. 1. The way of repairing is to cut off the common electrode COM at the two sides of the short circuit point S1 by laser to maintain the normal transmission of signals on the second data line DL(2). However, when another static electricity occurs to the third data line DL(3) and causes short circuit to the third data line DL(3) and the common electrode COM at a short circuit point S2 shown in FIG. 1, the third electrostatic discharge protection circuit 104(3) will not be coupled to the common electrode voltage Vcom if the common electrode COM is cut off by laser at the two sides of the short circuit point S2. Thus, the third electrostatic discharge protection circuit 104(3) is unable to operate normally. In other words, the second short circuit point S2 will make the display device 100 unreparable and become a defect.
Therefore, if more than two short circuits occur to the same signal line of the display device adopting the aforementioned configuration, then one of the short circuits can not be repaired. Consequently, the yield rate of the display device is decreased, thereby increasing the manufacturing cost of the display device.